The Story of a Concrete Sink

I’m guessing that most people have not put a hand on a concrete sink.

We use sinks in the kitchen, the bathroom, at work, in the store…sinks are everywhere. The sink is an ubiquitous element of our daily life. Frankly, most sinks are fairly boring. I think it’s one of those things that is almost an afterthought or at least something which doesn’t get much attention. After all, we have so many other elements to design with. If we focus on the bathroom for a minute, attention is on: the shower, the floor tile, the paint on the walls, the fixtures and even the vanity base, size and style of vanity. But where is the love for the sink?!


I’m going to give a brief explanation of what goes into our integral concrete sink and vanity tops.. And why should this be explained?  BECAUSE, if you have not experienced it, concrete is one of the coolest mediums to grace this planet. All I can do is speak from my point of view, and that is that concrete is special. Something about its sense of texture, its actual texture, the natural color variation, the variation that happens when it’s grouted and sanded, and the way that each piece comes out unique and different. I work with concrete every day and yet I am thrilled to pop each and every piece from its mold, smooth the edges to expose random and beautiful sand grains, and watch it transform with sealing coats. Every concrete piece is special and has had a lot of love in it’s making.

Here’s how we make a sink:


1) Forming the meat and potatoes

48" double sink fabric forming
48″ double sink fabric forming

Pictured right is 48″ double sink/vanity top. We are using felt here to generate an organically smooth flowing drain base. Personally, I like some nice hard edges in my pieces and so I’ve chosen to make the perimeter of the sink basin square and tight (next step). The idea is to pull felt over some cylindrical object (in this case some short lengths of PVC pipe) where the pipes form the local area around the drain. The felt is pulled away in a sloping fashion forming the slope to the drain as water sees it. It is important to remember that the mold construction is the opposite shape of what the final vessel will be. Everything is opposite; here we slope up but the actual sink will slope appropriately down to the drain.

The felt has been stretched and tacked down around the perimeter while the tubing under the felt has been appropriately affixed. After the fabric is taut and everything is in its place, resin is gently brushed into the felt. The felt absorbs the resin and becomes hard and stiff locking the shape without the need for tension on the felt. Several layers of resin lightened with fillers are added to the top to build up thickness for sanding the profile smooth.


2) Really forming the meat and potatoes

Fusing the fabric formed element to the PVC sides
Fusing the fabric formed element to the PVC sides

This isn’t the only way to skin a potato 😉 It’s just how I did it on this particular mold. I wanted the walls of the sink to be nice and tight -tight as in flat, square, no deviation. I used some PVC board pieces specially cut with draft angles on the table saw to form the walls and therefore the real vessel part of the sink.

The fabric formed part is only about 2″ deep- not too practical for sloshing water in. The PVC walls are about 3.5″ deep and are constructed in such a way to accept the now stiff fabric formed drain business end.The fabric formed section is bonded to the PVC vessel section with more resin, thickened resin and bubblegum!


3) Building a foundation

torsion box mold top
Bonding the webbing structure to the table top

This part is not absolutely necessary; all that’s needed is a flat surface that can be molded off of. In this case, I’m using a piece of particle board laminated with formica (Yes, other peoples [formica] countertops are our mold surfaces ;)) to make something called a torsion box. A torsion box is pretty much a stiff flat table designed to not bend.







4) Mixing concrete

face coat concrete
Face-coat applied to 48″ double sink mold

After everything is aligned, sealed, released, caulked, it is time to mix some concrete. The part pictured right was sprayed with a face-coat, which is a thin layer of concrete sprayed much like paint onto the mold surface. The layer is about 0.15″ thick and it’s used to produce a nice tight surface with very minimal porosity. After the face-coat is applied and appropriately stiff, a backer mix of structural concrete is applied. This is a combination of pouring and getting dirty with our hands to apply structural reinforcement to the face-coat and forming the bulk of the sink.



5) Cure. Pop. Appreciate.

48 inch double concrete sink
48″ double sink vanity fresh from the mold

The concrete we make is not your box store bag of premix It’s a bit fancier.  This allows us to pop the parts from the mold the next day, the parts are still curing and gaining strength, but they have enough strength to be handled around the shop. This part [pictured right], came right out of the mold-no prying, cursing or tears shed. The color variation is due to different concentrations of moisture, it is a young part after all. This part needs a few days to fully cure and release enough moisture for sealing. In the meantime it’s sanded and prepped for sealer.


6) Finishing: The end of the line

At this point a sealer is applied to make the otherwise porous and vulnerable concrete practical. Sealers have all types of different personalities and there are many of them. Sealers can be enhancing or not, reactive, filmy, penetrative, topical, etc, the list is long. We have used a few sealers but are really excited about the new Buddy Rhodes Reactive Polyurethane sealer. This sealer is relatively easy to use, offers great protection and looks killer. So after an appropriate cure time and moisture level, our sink part is brought into the sealing booth and in an oversimplified version of reality, comes out beautifully!

48" double vanity concrete sink
48″ double vanity sealed and complete

There you have it folks! All that’s left to do is pop some faucet holes in per the customers hardware and we are off to the races. I hope this has illuminated the process of making a custom concrete piece. It is time consuming, there are many steps and it requires a lot of experience to get right. But, when it’s right, it is magnificent.  I guarantee you will now think differently about bathroom sinks… and, if you want to lay your hand on one of ours you know where to find us.




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